Sensors are being included in more and more products, including but not limited to user-wearable devices. For example, an optical sensor that includes a light source and a light detector may be included in a wrist-worn health and/or activity monitor, wherein the optical sensor operate as photoplethysmography (PPG) sensor that enables the wrist-worn monitor to measure heart rate (HR) and heart rate variability (HRV) of the person wearing the monitor on their wrist. For another example, an optical sensor may be included in a smart phone, wherein the optical sensor operates as a proximity sensor that can be used to determine when the phone is being held close to a persons' ear, in response to which a touchscreen of the phone is disabled so that functions are not accidently triggered if the person's ear touches the touchscreen. With such optical sensors, it is desirable to reduce and preferably minimize or eliminate optical crosstalk. Additionally, it is desirable that such optical sensors are compact, since they are often included in portable devices in which small size and light weight are preferred. Similarly, for other types of sensors it is typically desirable that they are compact, especially when included in portable devices.